The Day of Blood involves mourning, fasting, sexual abstinence, self-mutilation, castration, and self-flagellation, all in memory of the grief encountered by Cybele. Some say this castration is done in memory of Attis, who had his genitals bitten off before he died by a pig. However, there is evidence that the castration is done in order to feel the pain of Cybele. Some priests would even dress like women before they castrated themselves. The bleeding caused is said to imitate menstruation.

The Taurobolium often occurs on this day, where initiates are bathed in the blood of a castrated bull to wash away their sins so they can be “born again.”